JP2014185976A - Treatment method of boric acid waste liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a treatment method of boric acid waste liquid, which suppresses deposition and accumulation on an inner wall surface of a tank, of a solid component originating from a thrown-in powdery chemical agent.SOLUTION: The treatment method of boric acid waste liquid includes the steps of: injecting a boric acid waste liquid into a tank and setting it to a prescribed temperature while agitating it; throwing a powdery chemical agent into the boric acid waste liquid while causing a cleaning liquid to flow on the inner wall surface of the tank; promoting reaction while agitating a mixture of the boric acid waste liquid and the powdery chemical agent in the tank; and discharging slurry produced by the reaction from the tank.

Description

  The present invention relates to a method for treating boric acid waste liquid, which includes a step of charging a powder medicine into a treatment tank.

In a pressurized water reactor (PWR), a large amount of boric acid solution used for power adjustment is discharged as waste liquid. Since this boric acid-containing waste liquid contains radionuclides, it is finally solidified with cement or the like and then disposed of.
Since the boric acid-containing waste liquid is acidic, an alkali metal element compound (for example, sodium hydroxide (NaOH)) is added as a neutralizing agent, and the boric acid-containing waste liquid is converted into a sodium borate waste liquid or the like.

By the way, boric acid interferes with the setting reaction of cement, causing a delay in hardening and a decrease in strength.
Therefore, a pretreatment is performed in which a powder agent of an alkaline earth metal element compound (for example, calcium hydroxide (Ca (OH) ₂ )) is added to the sodium borate waste liquid to precipitate boric acid as insoluble calcium borate. .

In order to suppress the increase in viscosity of the slurry produced by the precipitation of calcium borate, the sodium borate waste liquid after neutralization treatment was poured into a tank and set at 90 ° C. Has been introduced.
And this produced | generated slurry is dried after discharging | emitting from a tank, and the powdered calcium borate is cement-solidified (for example, patent document 1).

Japanese Patent No. 4208768

By the way, in the above-described tank, while the batch treatment of the sodium borate waste liquid is repeated, a situation occurs in which the solid content originating from the input calcium hydroxide adheres to and accumulates on the inner wall surface or the like.
If the amount of solids in the tank increases, problems such as a decrease in heating and heat transfer efficiency, a decrease in control accuracy of the liquid level gauge, a decrease in stirring efficiency due to the impeller, and excessive drug administration due to an increase in the tank liquid level May occur.

  As described above, when the amount of solid content in the tank increases, not only the operational stability of the sodium borate waste liquid treatment is impaired, but also there is a concern about an increase in the exposure amount of workers due to frequent maintenance.

  The present invention has been made in consideration of such circumstances, and provides a method for treating boric acid waste liquid in which the solid content originating from the charged powder drug is prevented from adhering to and accumulating on the inner wall surface of the tank. The purpose is to do.

  In the method for treating boric acid waste liquid according to the present invention, the step of injecting the boric acid waste liquid into the tank and setting it to a predetermined temperature while stirring, and the powdered chemical agent in the boric acid waste liquid while flowing the cleaning liquid on the inner wall surface of the tank And a step of causing the reaction to proceed while stirring the boric acid waste liquid and the powder drug mixture in the tank, and a step of discharging the slurry generated by the reaction from the tank. Features.

  According to the present invention, there is provided a method for treating boric acid waste liquid in which solid content originating from the charged powder medicine is prevented from adhering to and accumulating on the inner wall surface of the tank.

(A) The longitudinal cross-sectional view which shows 1st Embodiment of the tank applied to the processing method of the boric-acid waste liquid which concerns on this invention, (B) The same and horizontal sectional view. The timing chart explaining the processing method of the boric acid waste liquid in 1st Embodiment. The longitudinal cross-sectional view which shows 2nd Embodiment of the tank applied to the processing method of the boric acid waste liquid which concerns on this invention. The table | surface which shows the verification result of the processing method of the boric acid waste liquid in 2nd Embodiment.

(First embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
As shown in FIG. 1, a tank 10 applied to the boric acid waste liquid treatment method according to the first embodiment includes a waste liquid tank 11 for injecting boric acid waste liquid 12 into the tank, and the boric acid waste liquid 12 at a predetermined temperature. Heater 13, a chemical tank 14 for charging the powder chemical into the boric acid waste liquid 12 inside the tank, a cleaning tank 15 for holding the cleaning liquid 23 that flows to the inner wall surface 10 a of the tank, the boric acid waste liquid and the powder chemical The mixture is composed of a stirrer 16 that advances the reaction while stirring the mixture in the tank, and a discharge unit 17 that discharges the slurry generated by the reaction from the tank 10.

  The tank 10 has a cylindrical shape and a round bottom shape, which is excellent in cleanability, but may be a square shape, and the tank shape is not particularly limited. A manhole 18 is provided on the upper surface of the tank 10 to allow workers to enter and exit the tank 10.

The boric acid waste liquid 12 injected into the tank from the waste liquid tank 11 is neutralized by mixing sodium hydroxide (NaOH) with the waste liquid of the boric acid solution used for adjusting the output of the pressurized water reactor, and further heating. A concentrated sodium borate waste liquid is assumed.
Here, the neutralizing agent used is not limited to sodium hydroxide, and other alkali metal element compounds (for example, lithium hydroxide, potassium hydroxide, or a mixture thereof) are also preferably used. it can.
However, the boric acid waste liquid 12 treated in each embodiment is included in the case where the neutralization treatment is not performed, and the boric acid concentration in the waste liquid is not particularly limited.

It is assumed that the powdered medicine charged from the chemical tank 14 to the boric acid waste liquid 12 inside the tank is calcium hydroxide (Ca (OH) ₂ ).
This is because it is assumed that the boric acid waste liquid 12 is finally subjected to cement solidification treatment, so that boric acid that interferes with the setting reaction of the cement and causes a delay in hardening or a decrease in strength is precipitated as calcium borate. It is for insolubilization.

Here, the powder medicine for precipitating boric acid in the waste liquid as borate is not limited to sodium hydroxide, and other alkaline earth metal element compounds (for example, magnesium hydroxide) are also preferably used. Can do.
In addition, the powder drug to be introduced in each embodiment is also included in the case where there is no action of precipitating boric acid in the waste liquid as borate as described above.

The heater 13 heats the boric acid waste liquid 12 (sodium borate waste liquid) injected into the tank 10 to a temperature higher than 85 ° C. (for example, 90 ° C.).
Then, a predetermined amount of powder medicine (Ca (OH) ₂ )) charged from the medicine tank 14 is added, and the mixture of the boric acid waste liquid 12 and the powder medicine is stirred by the stirrer 16 for a predetermined time (three hours or more). To advance. Thereafter, the slurry generated by the reaction is cooled to a predetermined temperature (about 70 ° C.) by a cooling device (not shown) or natural cooling and discharged from the discharge unit 17.
Thus, by treating the boric acid waste liquid 12 with a chemical or heat treating it, the waste liquid properties can be stabilized and an increase in viscosity can be suppressed.

The cleaning tank 15 supplies the stored cleaning liquid to an annular pipe 21 provided coaxially with the tank 10. The annular pipe 21 injects the cleaning liquid 23 radially downward from the plurality of ejection holes 22 to flow to the tank inner wall surface 10a.
The sprayed cleaning liquid 23 is set to a temperature of 30 ° C. or higher, preferably 60 ° C. or higher in order to improve the cleaning effect.

The distance from the plurality of ejection holes 22 of the annular pipe 21 to the tank inner wall surface 10a is preferably set to 5% or less with respect to the tank diameter.
If the distance from the ejection hole 22 to the tank inner wall surface 10a exceeds 5% with respect to the tank diameter, the flow rate of the cleaning liquid traveling along the tank inner wall surface is lowered, and the cleaning efficiency is lowered.

It is desirable that 30 or more ejection holes 22 are provided at equal intervals over the entire circumference of the annular pipe 21.
If the number of the ejection holes 22 is smaller than this and the interval is widened, the ejected cleaning liquid 23 does not spread over the entire tank inner wall surface 10a, and a gap is formed, which is not preferable.
Further, when the cleaning liquid 23 is ejected perpendicularly to the tank inner wall surface 10 a, the cleaning efficiency is lowered due to rebounding. Therefore, the ejection hole 22 is desirably provided slightly below the annular pipe 21.

In each embodiment, the portion where the powder drug adheres to the inner wall surface of the tank 10 includes (1) liquid surface upper part (gas phase part), (2) liquid surface interface (gas phase, liquid phase boundary part) and (3 ) It is roughly classified into three places below the liquid level (in the liquid phase).
Since the factors causing the powder drug to adhere to each inner wall portion are different, different cleaning strategies are considered for each to reduce the amount of adhesion.

  The adhesion of the powder drug on the upper surface of the liquid (1) tends to adhere in a large amount when the powder drug is charged. For this purpose, it is effective to prevent the adhesion by flowing the cleaning liquid 23 to the tank inner wall surface 10a so as to make it a wet wall state while washing off the powder medicine.

Further, the boric acid waste liquid 12 has a property of increasing the viscosity when concentrated. When the water is vaporized and adhered to the upper part of the inner wall surface by the stirring action after the tank is added and the water vaporizes to increase the viscosity, the boric acid waste liquid 12 is subsequently added by the glue action Powder drug adheres.
In order to prevent such boric acid waste liquid 12 from scattering to the upper part of the liquid surface, the rotational speed of the stirrer 16 is reduced as much as possible, and the cleaning liquid 23 is allowed to flow to the tank inner wall surface 10a before and after the powdered chemical is charged. It is effective to wash off.

(2) When the boric acid waste liquid 12 is poured into the tank and stirred, the adhesion of the powdered chemical at the liquid surface interface of the boric acid waste liquid 12 that has become highly viscous on the inner wall surface of the tank in contact with the interface due to the undulation of the liquid surface. It is based on the fact that a film is formed, and the powdered drug charged therein adheres.
In order to prevent the film of boric acid waste liquid 12 having increased viscosity in this way from being formed on the inner wall surface of the tank, it is necessary to reduce the number of revolutions of the agitator 16 as much as possible to suppress the undulation of the liquid level. .
Furthermore, it is effective to wash the deposits by flowing the cleaning liquid 23 to the tank inner wall surface 10a before and after the powdered medicine is charged.

In addition, the adhesion of the powder drug at the liquid level interface in (2) also depends on the property of calcium hydroxide (powder drug) that changes into calcium carbonate and becomes insoluble under high humidity conditions in the air.
It is estimated that the calcium carbonate changed from this calcium hydroxide becomes a base point of the deposit on the inner wall surface of the tank.
Thus, in order to prevent the change from calcium hydroxide to calcium carbonate, the gas phase inside the tank 10 is replaced with an inert gas such as nitrogen.

In order to prevent the powder drug from adhering to the lower part of the liquid level in (3), it is effective to flush the tank inner wall surface 10a by flowing the cleaning liquid 23 each time the slurry is discharged from the discharge part 17 of the tank 10.
That is, for each batch process, the tank inner wall surface 10a is washed away with the cleaning liquid 23 and then the next batch process is performed, and the boric acid waste liquid 12 is injected from the waste liquid tank 11 into the tank.

Furthermore, the deposits on the inner wall surface 10a accumulated as a result of repeated batch processing of the boric acid waste liquid 12 in the tank 10 need to be thoroughly cleaned from the viewpoint of reducing the exposure dose of workers approaching the tank during regular inspection. is there.
Specifically, the tank 10 is filled with a waste of boric acid solution periodically generated at a power plant of a pressurized water reactor (PWR) as a cleaning liquid, and the stirrer 16 is operated to perform thorough cleaning.
The cleaning agent used in this thorough cleaning is not limited to the boric acid solution, and dilute sulfuric acid or the like can be used, but there is a problem that a new waste disposal target is generated.

Based on the timing chart of FIG. 2 (see FIG. 1 as appropriate), the boric acid waste liquid treatment method in the first embodiment will be described. This timing chart shows one batch processing process.
First, boric acid waste liquid (sodium borate solution) maintained at about 70 ° C. in the waste liquid tank 11 is poured into the tank 10 and heated while stirring to set a predetermined temperature (about 90 ° C.).
The stirring in the temperature rising process of the injected boric acid waste liquid is performed in order to make the temperature in the tank uniform.
Therefore, in the stirring of the boric acid waste liquid before the start of the charging of the powder medicine (Ca (OH) ₂ ), the rotation speed of the stirrer 16 is adjusted to a low speed so that the undulation at the interface is within ± 2 mm.

When the undulation at this interface exceeds ± 2 mm, the boric acid waste liquid 12 scatters to the gas phase and adheres to the inner wall surface of the tank, further concentrates, and promotes the adhesion of the powder medicine (Ca (OH) ₂ ) to be introduced later. There is a fear.
In addition, it is not preferable to reduce the stirring rotation speed to such an extent that no undulation is observed, because the temperature of the waste liquid in the tank becomes non-uniform and bumping may occur in some cases.

When the waste liquid temperature in the tank reaches 90 ° C., the powdered chemical (Ca (OH) ₂ ) is charged from the chemical tank 14 to the tank 10.
In the stirring of the boric acid waste liquid after the start of the charging of the powder drug, the number of revolutions of the stirrer 16 is adjusted at a high speed so that the undulation of the interface is within ± 50 mm, and the reaction is effectively advanced.
After the rotation speed of the stirrer 16 is switched to a high speed, scattering of the waste liquid on the tank inner wall surface 10a is inevitable.

Therefore, the cleaning liquid 23 is caused to flow on the inner wall surface 10a of the tank during the period when the powdered chemical (Ca (OH) ₂ ) is added to the boric acid waste liquid 12.
Note that the flow rate of the cleaning liquid sprayed from the nozzle hole 22 of the annular pipe in the pre-stage A or post-stage C of the period shown in FIG. The flow rate during period B between A and the subsequent stage C was set to a low speed of 0.8 m / s or more and less than 6 m / s.

When the flow rate of the cleaning liquid in the pre-stage A or the post-stage C is set to be less than 6 m / s, the powder drug tends to adhere to the tank inner wall surface 10a and remain.
If the flow rate in period B exceeds 6 m / s, the waste liquid in the tank may increase due to the supply of the cleaning liquid, and if it falls below 0.8 m / s, the wet wall state over the entire surface of the tank inner wall surface 10a cannot be maintained.

In this period B, the powdered drug is added over 3.5 to 7 minutes. However, since a film of the cleaning liquid is generated on the tank inner wall surface 10a, adhesion is suppressed.
However, it is unavoidable that a band-like adhesion having a width of several millimeters is inevitably generated at the liquid interface portion of the tank inner wall surface 10a by the action of stirring in the period B.
For this reason, in the subsequent stage C of the period B, the flow rate is increased again to perform cleaning for a short time, and the residual deposits on the interface portion of the tank inner wall surface are washed away.
In addition, although the example in which the flow rate of the cleaning liquid is set to be high in both the pre-stage A and the post-stage C of the injection period of the powder drug is exemplified, it is not an essential requirement to set the flow rate so high.

After stopping the injection of the powder medicine and the spraying of the cleaning liquid, the mixture of the boric acid waste liquid and the powder medicine (Ca (OH) ₂ ) is kept at a predetermined temperature (90 in the tank while maintaining the rotation speed of the stirrer 16 at a high speed. C.) The reaction is allowed to proceed with stirring for a predetermined time (8 hours).
Then, the temperature of the slurry generated by the reaction is lowered while maintaining high-speed stirring until the temperature (74 ° C.) suitable for discharging from the tank 10 is reached.

In a long process such as advancing the reaction and lowering the temperature, deposits are generated on the tank inner wall surface 10a over the gas phase portion, the liquid surface interface portion, and the liquid surface lower portion. Furthermore, a component (calcium borate) insolubilized by the reaction is contained in a large amount in the waste liquid.
In this state, when the waste liquid is discharged from the tank and the boric acid waste liquid of the next batch is injected from the waste liquid tank 11, the residual powder in the previous batch becomes the core, and the newly added powder medicine adheres. And become the starting point for growth.

Therefore, the cleaning liquid is caused to flow on the inner wall surface during a period in which the waste liquid is discharged from the tank 10.
Specifically, in the waste liquid discharge stage D, the stirring speed is reduced, and the cleaning liquid is flowed to the tank inner wall surface 10a for 5 seconds at a flow rate of 6 m / s or higher for cleaning.
As a result, the residual deposits of the previous batch are washed away, and in the next treatment of the boric acid waste liquid of the next batch, the number of nuclei from which the powder drug adheres and grows is reduced.

Furthermore, the boric acid waste liquid treatment is recommended by repeating the batch treatment shown in FIG. 2 a plurality of times in succession.
When the treatment of boric acid waste liquid is stopped for a while due to periodic inspection or the like, in order to thoroughly clean the inside of the tank 10, after discharging the waste liquid in the final batch, the tank 10 is filled with the boric acid solution and stirred to Complete removal of deposits 10a.
The boric acid solution can be injected into the tank 10 from any one of the waste liquid tank 11, the chemical tank 14, the cleaning tank 15, and the manhole 18.

Calcium hydroxide, which is the main component of the deposit, has a very low solubility (0.17 g / 100 cm ³ (25 ° C.)), and has a property that the solubility decreases when the temperature is raised. It is a difficult substance.
This is because the next reaction (1) is slow, and in order to accelerate this reaction, it is necessary to remove the product on the right side of the formula (1) by changing it to another substance.
Ca (OH) ₂ (adhesion solid content) + H ₂ O (liquid) = Ca ²⁺ (dissolution) + 2OH ⁻ (1)

The effect of changing the product on the right side of this formula (1) to another substance cannot be obtained with warm water or sodium hydroxide, but boric acid, which is a weak acid, is produced by water produced as shown in formula (2). It has the action of extracting acid ions (OH ⁻ ).
Thus, by using the boric acid solution, the equilibrium reaction of the formula (1) can always be moved to the right side, and the dissolution reaction of the deposit of calcium hydroxide can proceed.
OH ⁻ + H ₃ BO ₃ (liquid) = B (OH) ⁴⁻ (2)

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIG.
FIG. 3 is a longitudinal sectional view showing a basic configuration of the tank 10 applied to the boric acid waste liquid treatment method according to the second embodiment. 3, parts having the same configuration or function as those in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted.

In the tank 10 applied to the second embodiment, the cleaning liquid that flows to the inner wall surface is supplied from the inside of the tank 10 through the circulation mechanism 19 that is connected to the annular pipe 21 by the circulation pipe 24 through the pump 20. It is characterized by being.
Thereby, unlike the case of the first embodiment, there is no added amount of cleaning liquid in the total discharge amount from the tank 10.
The injection of the cleaning liquid 23 onto the inner wall surface 10a is not limited to the one using the illustrated annular pipe 21, but may be based on a tube pump passing through the tank.

[Example 1]
Next, Example 1 in which the effect of the first embodiment shown in FIGS. 1 and 2 is confirmed will be described.
The tank used has a round bottom shape with dimensions of about 1200 mmφ × 1350 mmH, and the internal capacity is nominally 1 m ³ .
The annular pipe for cleaning provided at the uppermost part of the tank has 30 3 mmφ ejection holes arranged uniformly on the inner wall surface side of the tank.
Warm water set at 60 ° C. is ejected from the washing tank connected to the pipe by a pump into the ejection hole of the annular pipe.

In this tank, about 400 kg of sodium borate aqueous solution that was previously adjusted to a temperature of about 70 ° C., a boric acid concentration of about 12 wt%, and a NaOH / Na molar ratio of 0.3 was simulated by simulating the waste liquid injected from the waste liquid tank. It has been thrown.
In the process of raising the temperature of the aqueous solution of sodium borate, which is a simulated waste liquid, from 70 ° C. to 90 ° C., the rotation speed of the stirrer was set at 140 min ⁻¹ (low rotation speed) and stirred.
Under the setting condition of the rotation speed of the stirrer, the undulation of the interface liquid level was adjusted to ± 2 mm, and the simulated waste liquid was prevented from scattering and the temperature unevenness of the liquid temperature was eliminated.

When the simulated waste liquid reached 90 ° C., warm water was injected from the annular pipe at a flow rate of 80 L / min (flow rate 6 m / s) for 5 seconds to wash the simulated waste liquid adhering to the inner wall surface of the tank.
Subsequently, the rotation speed of the stirrer was set to 350 min ⁻¹ (high rotation speed), and adjustment was made so that the interfacial liquid level ripple was ± 50 mm.
Immediately after setting the stirrer at a high rotational speed, 26 kg of powdered drug (Ca (OH) ₂ ) was charged into the tank over a period of 3.5 min from a chemical tank installed at the top of the tank, and the Ca / B molar ratio was 0. Adjusted to 45.

Simultaneously with the start of the charging of the powder medicine, hot water was injected from the annular pipe at a flow rate of 10 L / min (flow rate 0.8 m / s) and continued until the end of the charging.
Simultaneously with the completion of the charging of the powder medicine, warm water was sprayed from the annular pipe at a flow rate of 80 L / min (flow rate: 6 m / s) for 5 seconds to clean the inner wall surface of the tank.
Immediately after this, when the internal situation was visually observed from the manhole at the top of the tank, no deposits were found on the gas phase portion and the interface portion of the tank inner wall surface.

  The simulated waste liquid was set at 90 ° C and the stirring was set at a high rotational speed, and continued for 8 hours. Then, the temperature was lowered to 74 ° C, the stirring was set at a low rotational speed, the heater was stopped, and the discharge part at the bottom of the tank was opened to react. The liquid was drained.

Immediately after the reaction solution was discharged, warm water was injected from the annular pipe at a flow rate of 80 L / min (flow rate: 6 m / s) for 5 seconds to clean the inner wall surface of the tank.
When the internal situation was observed from the manhole at the upper part of the tank, immediately after the reaction liquid was discharged, an adhering band with a height of about 50 mm was formed on the liquid interface part of the inner wall surface of the tank, and a waste liquid with a height of about 300 mm in the gas phase part. Adherents due to scattering were observed, and insoluble particles were observed in the liquid phase part.
On the other hand, after washing the inner wall surface of the tank with warm water, deposits on the gas phase portion and the interface in the tank were almost removed, and the liquid phase portion was completely removed by washing.

Although the simulated waste liquid processed in the tank in Example 1 is about 420 L, the total amount of discharge is further added with about 60 L of cleaning liquid. With this amount of addition, the effect on the subsequent drying process (not shown) is negligible.
Furthermore, as a result of repeating the batch treatment three times under the above conditions, no growth of deposits was observed in the tank.

As an additional example, the initial charge amount of the simulated waste liquid into the tank is increased to about 730 L, and the powder agent (Ca (OH) ₂ ) is increased to 45 kg for 7 min in order to make the Ca / B molar ratio 0.45 common. The experiment was conducted under the same conditions as described above, except that the tank was put into the tank.
As a result, deposits on the gas phase portion and the interface portion of the inner wall surface of the tank were almost removed, and the liquid phase portion was completely washed away.

Thereby, even if the injection amount of the waste liquid increased, it was confirmed that there was no difference in the adhesion suppression effect and the washing removal effect of the solid content and it was good.
In this additional example, the simulated waste liquid processed in the tank is about 770 L, and the total amount of discharge is further added with about 96 L of cleaning liquid. With this amount of addition, the effect on the subsequent drying process (not shown) is negligible.

As an additional example, the experiment was performed under the same conditions as described above, except that the cleaning liquid that was 60 ° C. warm water in the above setting was set to 30 ° C. warm water.
As a result, the adhered particles in the liquid phase portion on the inner wall surface of the tank were almost removed.
Some solid content remains in the gas phase part and the interface part on the inner wall surface of the tank, which is slightly inferior in cleaning performance compared with the case where the temperature is set to 60 ° C., but it has a certain solid content suppression and cleaning effect. It was confirmed that

[Comparative Example 1]
The comparative example 1 which abbreviate | omitted the process which becomes the characteristic of above-described Example 1 is shown.
In the same manner as in Example 1, about 400 kg of simulated waste liquid of sodium borate aqueous solution adjusted to a temperature of about 70 ° C. in advance is put into the tank.
Thereafter, in the process of raising the temperature of the sodium borate aqueous solution from 70 ° C. to 90 ° C., the stirring speed is set to 350 min ⁻¹ (high rotation speed) and stirred, and the swell of the interface liquid level is set to ± 50 mm. It was adjusted.

When the simulated waste liquid reached 90 ° C., 26 kg of powdered drug (Ca (OH) ₂ ) was charged into the tank over 12 min from the drug tank with the stirrer set at a high rotational speed.
At this time, when the manhole at the upper part of the tank was opened and the internal state was observed, the powdered drug adhered to the circumference of the circumference of the inner wall surface of the tank with a thickness of about 10 mm.

The simulated waste liquid was kept at 90 ° C. and the stirring was set at a high rotational speed for 8 hours, then the temperature was lowered to 74 ° C., and the discharge part at the bottom of the tank was opened to discharge the reaction liquid.
At this point, when the internal situation is observed from the manhole at the upper part of the tank, the adhesion of the gas phase portion on the inner wall surface of the tank is increased by the amount of adhesion from immediately after the powdered drug is added due to scattering during stirring, and 300 to Adhesion spread over the entire circumference at a height of 500 mm.

In addition, a band having a height and thickness of about 10 mm spread all around the interface portion of the inner wall surface of the tank. In addition, insoluble particles were thinly attached to the entire liquid phase portion.
Furthermore, as a result of repeating batch processing 3 times on the said conditions, the deposit | attachment grew in any location.

[Example 2]
Next, Example 2 which confirmed the effect of 2nd Embodiment shown by FIG. 3 is demonstrated.
The table shown in FIG. 4 is a result of demonstrating the boric acid waste liquid treatment method in Example 2, and the result of washing the inner wall surface of the tank to which the powder medicine was adhered with the circulation flow rate of the circulation mechanism washed with room temperature tap water. Is shown.
In addition, when the circulation flow rate was set to 80 L / h, the jet flow velocity of the annular pipe was 6 m / s.
Example 2 uses a tank having the same equipment as shown in Example 1, a simulated waste liquid, and a powdered medicine having the same composition as in Example 1 except that it has a circulation mechanism for waste liquid in the tank.

The cleaning liquid was sprayed at a flow rate of 20 L / min and 30 L / min for 3 minutes to about 2 kg of deposits, but some of the deposits could not be removed (Evaluation ×).
When the cleaning liquid was sprayed at a flow rate of 50 L / min on the deposit of about 2 kg, the deposit could be removed in 1 minute, but the required time was long (evaluation Δ).
When the cleaning liquid was sprayed at a flow rate of 80 L / min and 100 L / min on the deposit of about 2 kg, the deposit could be removed in 5 seconds (evaluation ◯).
When the cleaning liquid was sprayed at a flow rate of 80 L / min on the deposit of about 6 kg, the deposit could be removed in 15 seconds (evaluation ○).

Although the table shown in FIG. 4 shows the result of using room temperature tap water as the cleaning liquid, it is evaluated as ◯ because there is no noticeable solid content on the inner wall surface of the tank, Insoluble particles sometimes adhered to the entire inner wall.
Therefore, the cleaning liquid was switched to hot water at 60 ° C., and the cleaning liquid was sprayed at a flow rate of 80 L / min against 2 kg of deposits. The deposits and insoluble particles could be removed in 5 seconds.

Example 3
At the end of repeated batch processing, the effect of thoroughly cleaning the inner wall of the tank was examined.
In a lab scale device, simulated waste liquid was adjusted, powdered chemicals were added, stirred at 90 ° C. for 8 hours, and stirred and held at 74 ° C. for 18 hours in succession for 3 batches, imitating the tank inner wall surface. Deposits were formed on the stainless steel surface.

After discharging the simulated waste liquid from this lab scale device, 60-70 ° C. warm water was added and stirring washing was performed for 5 hours, but deposits could not be remarkably removed.
Deposits were formed by the same method as above, sodium borate solution was added, and stirring and washing was performed in the same manner, but the deposits could not be removed significantly.

  Therefore, when deposits were formed by the same method as above, boric acid water (concentrations of 10000 and 21000 ppm) set to 60 to 30 ° C. was added and stirring and washing were performed for 2 to 4 hours, it was remarkably dissolved. Stainless steel glossy surface appeared.

Next, since this used boric acid water becomes a waste, the processing method was examined.
The washing liquid was heated to 74 ° C. and sodium hydroxide was added to adjust Na / B = 0.3.
Further, the liquid temperature was heated to 90 ° C., and calcium hydroxide was adjusted to Ca / B = 0.45 and held for 8 hours. As a result, calcium borate was generated and insolubilization treatment could be performed.
From this result, waste of boric acid water generated after thorough cleaning can be treated without any problem as with sodium borate waste liquid.

  According to the boric acid waste liquid treatment method of at least one embodiment described above, a solid chemical originating from the charged powder medicine is included by including the step of feeding the powder medicine while flowing the cleaning liquid on the inner wall surface of the tank. Minutes are prevented from adhering to and accumulating on the inner wall surface of the tank.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 10 ... Tank, 10a ... Inner wall surface, 11 ... Waste liquid tank, 12 ... Boric acid waste liquid, 13 ... Heater, 14 ... Chemical tank, 15 ... Cleaning tank, 16 ... Stirrer, 17 ... Discharge part, 18 ... Manhole, 19 ... Circulation mechanism, 20 ... pump, 21 ... annular pipe, 22 ... jet hole, 23 ... cleaning liquid, 24 ... circulation piping.

Claims (13)

Injecting boric acid waste liquid into the tank and setting it to a predetermined temperature while stirring;
Introducing a powdered chemical into the boric acid waste liquid while flowing a cleaning liquid on the inner wall surface of the tank;
Advancing the reaction while stirring the boric acid waste liquid and the powder drug mixture in the tank;
Discharging the slurry generated by the reaction from the tank, and treating the boric acid waste liquid. In the processing method of the boric acid waste liquid according to claim 1,
A boric acid waste liquid treatment method, wherein a flow rate of the cleaning liquid is set high in at least one of a pre-stage and a post-stage of a period in which the powder drug is added to the boric acid waste liquid. In the processing method of the boric-acid waste liquid of Claim 1 or Claim 2,
A boric acid waste liquid treatment method, wherein a cleaning liquid is caused to flow on the inner wall surface during a period of discharging the slurry from the tank. In the processing method of the boric-acid waste liquid of any one of Claims 1-3,
The boric acid waste liquid is neutralized with an alkali metal element compound discharged from a nuclear facility,
The said powder chemical | medical agent is an alkaline-earth metal compound, The processing method of the boric-acid waste liquid characterized by the above-mentioned. In the processing method of the boric-acid waste liquid of any one of Claims 1-4,
The boric acid waste liquid treatment method is characterized in that the boric acid waste liquid is stirred before the start of charging of the powdered drug, and the number of revolutions of the stirrer is adjusted so that the undulation of the interface is within ± 2 mm. In the processing method of the boric-acid waste liquid of any one of Claims 1-5,
The boric acid waste liquid treatment method is characterized in that the boric acid waste liquid is stirred after the start of charging of the powdered drug so that the rotational speed of the stirrer is adjusted so that the undulation of the interface is within ± 50 mm. In the processing method of the boric-acid waste liquid of any one of Claims 1-6,
The method for treating boric acid waste liquid, wherein the cleaning liquid to be flowed to the inner wall surface is ejected radially downward from a plurality of ejection holes of an annular pipe coaxially provided in the tank. In the processing method of the boric acid waste liquid according to claim 7,
A method for treating boric acid waste liquid, wherein a distance from a plurality of ejection holes of the annular pipe to an inner wall surface of the tank is 5% or less with respect to a tank diameter. In the processing method of the boric acid waste liquid according to claim 7 or claim 8,
The flow rate of the cleaning liquid injected from the nozzle hole in the annular pipe in the first stage or the second stage of the period when the powder drug is introduced is 6 m / s or more, and the flow rate in the period is 0.8 m / s or more and 6 m / s. The boric acid waste liquid treatment method is characterized by being set to less than s. In the processing method of the boric-acid waste liquid of any one of Claims 1-9,
The method for treating boric acid waste liquid, wherein the cleaning liquid is supplied from the outside of the tank. In the processing method of the boric acid waste liquid according to claim 10,
The method for treating boric acid waste liquid, wherein the cleaning liquid is water whose temperature is set to 30 ° C. or higher. In the processing method of the boric-acid waste liquid of any one of Claims 1-9,
The method for treating boric acid waste liquid according to claim 1, wherein the cleaning liquid to be flowed to the inner wall surface is circulated and supplied from the inside of the tank. In the processing method of the boric-acid waste liquid of any one of Claims 1-12,
After the step of discharging the slurry, the boric acid waste liquid treatment method further comprises a step of filling the tank with a boric acid solution and stirring to remove deposits on the inner wall surface.

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